This invention relates to rail wheel grippers, which term is intended herein to include both holding apparatus for moving vehicles, of the kind in which one or more wheels of a vehicle running on a rail track is contacted on its opposite side faces by opposed surfaces of clamping members that are mounted separately from the vehicle and are urged inwardly towards each other by operating means so as to grip the wheel between the. Such rail wheel grippers mounted on the track may be adapted to hold a vehicle stationary in a desired location or to act as a squeeze retarder in the marshalling of rail vehicles.
It is known to construct such wheel grippers in the form of calipers, comprising two opposed arms on opposite sides of the rail and pivoted at their lower ends to swing upwardly and inwardly. Such a mechanism, however requires considerable clearance both for its instalation and for its operation, In particular, in order to grip a wheel some way above its bottom contact point with the rail, the caliper arms must be relatively long and occupy a correspondingly wide span when pivoted downwards to their rest positions, while care must be taken to ensure that there is sufficient clearance between the wide arc they sweep as they are raised and the running gear of the vehicles on which they are intended to operate.